A shotgun is a firearm that uses the energy of a shotgun shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug. One popular type of shotgun is the repeating pump-action shotgun. A conventional pump-action shotgun is one in which the handgrip or forend can be pumped back and forth in order to cycle the action to eject a spent round of ammunition and to chamber a fresh one. A pump-action shotgun is typically fed from a tubular magazine underneath the barrel, which also serves as a guide for the movable forend. The rounds are fed one by one into the action through a port in the receiver, where they are lifted by a lever called the shell lifter and are pushed forward into the chamber by the bolt. A pair of interrupters at the rear of the magazine holds the rounds in place to facilitate feeding of one shell at a time.
The forend is connected to the bolt by one or two bars (two bars are considered more reliable because they provide symmetric forces on the bolt and pump and reduce the chances of binding). The motion of the bolt back and forth in a tubular magazine model also operates the shell lifter, which lifts the shells from the level of the magazine to the level of the barrel. Modern pump shotgun designs have a safety feature called a trigger disconnector, which disconnects the trigger from the sear as the bolt moves back, so that the trigger must be released and pulled again to fire the shotgun after it closes.
After firing a round, the bolt is unlocked and the forend is free to move. The shooter pulls back on the forend to begin the operating cycle. The bolt unlocks and begins to move to the rear, which extracts and ejects the empty shell from the chamber, cocks the hammer, and begins to load the new shell. In a tubular magazine design, as the bolt moves rearwards, a single shell is released from the magazine and is pushed backwards to come to rest on the shell lifter.
As the forend reaches the rear and begins to move forward, the shell lifter lifts up the shell, lining it up with the barrel. As the bolt moves forward, the round slides into the chamber, and the final portion of the forend's travel locks the bolt into position. A pull of the trigger will fire the next round, where the cycle begins again.
A shotgun is generally a smoothbore firearm, which means that the inside of the barrel is not rifled. The shot pellets from a shotgun spread upon leaving the barrel, and the power of the burning charge is divided among the pellets, which means that the energy of any one ball of shot is fairly low. Shotguns are very popular for bird hunting. Shotguns can also be used for more general forms of hunting with slugs. Shotguns are often used with rifled barrels in locations where it is not lawful to hunt with a rifle. Typically, a sabot slug is used in these barrels for maximum accuracy and performance. However, the relatively low muzzle velocity of slug ammunition, and the blunt, poorly streamlined shape of typical slugs that causes them to lose velocity very rapidly compared to rifle bullets, limits the effectiveness of shotguns with many types of game.
Therefore, a need exists for a new and improved shotgun ammunition conversion system that converts a repeating shotgun into a repeating rifle capable of firing centerfire and rimfire cartridges. These larger caliber and higher-powered cartridges relative to shotgun shells enable shotgun users to hunt a wider variety of game while in the field without requiring the user to carry two separate guns. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the shotgun ammunition conversion system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of converting a repeating shotgun into a repeating rifle capable of firing centerfire and rimfire cartridges.